JP6635235B1 - Lap laser welded joint, manufacturing method of lap laser welded joint, and skeletal parts for automobile - Google Patents

Abstract

It is an object of the present invention to provide a lap laser welded joint, a method of manufacturing the lap laser welded joint, and an automobile skeleton component having the lap laser welded joint. The present invention is a lap laser welded joint having a welded portion joined by lap laser welding to a lap portion in which a plurality of steel plates are overlapped, and the weld portion is a main weld portion penetrating the steel plate of the lap portion. And a final weld having a crater formed at one end of the main weld, and the weld satisfies the equations (1) to (4).
L ≧ 15.0 (1)
10.0 ≧ L2 ≧ 2l _c (2)
t1 ≧ 2d _c (3)
w _c > d _c (4)

Description

  The present invention relates to a lap laser welded joint, a method of manufacturing the lap laser welded joint, and a skeleton part for an automobile having the lap laser welded joint.

  Conventionally, resistance spot welding has been used for welding structural members of an automobile having a flange portion. However, resistance spot welding is problematic in that it takes a long time to perform welding, that the amount of heat generated by shunting decreases, and that the pitch cannot be narrowed, and that there is a spatial restriction due to the gun provided in the welding machine. There's a problem. In order to solve these problems, in recent years, use of lap laser welding has been studied in addition to conventional resistance spot welding. Here, lap laser welding refers to a welding method of irradiating a laser beam to a surface of a plurality of superposed steel sheets and joining the steel sheets.

  In lap laser welding, a molten portion (welded portion) is formed by irradiating a laser beam on the surface of multiple superposed steel sheets in a linear shape and melting and solidifying the irradiated part of the steel sheet irradiated with the laser beam. Is done. Thereby, the superposed steel plates are joined to obtain a lap laser welded joint. However, in the case of lap laser welding, cracks tend to occur on the end side of the linear fusion zone, and when cracks occur, there is a problem that the cracks propagate over the entire length of the fusion zone. When cracks are generated and propagated in the weld metal, static strength such as shear and peel strength of the lap laser welded joint decreases, and there is a concern that fatigue strength may significantly decrease due to the propagation of cracks from cracks. You. In recent years, for automobile body parts, particularly skeletal parts, higher strength high-strength steel sheets have been used to improve body strength and rigidity, and the static strength and fatigue of joints due to cracks in welds have been increasing. The reduction in strength is a serious problem.

  Accordingly, various techniques have been disclosed as methods for suppressing the occurrence and propagation of lap laser welding cracks that occur when laser welding is performed on superposed steel sheets.

  For example, Patent Literature 1 discloses a technique for preventing welding cracks by projecting a steel plate below a lap weld and setting a welding start position at a position away from an end of a flange. Patent Literature 2 discloses a technique of irradiating a laser obliquely to an end of a superposed surface to prevent a weld crack. Patent Documents 3 and 4 disclose a technique for preventing welding cracks by reheating or welding the once welded portion and the periphery of the welded portion. Patent Literature 5 discloses a technique for preventing the occurrence of weld cracks by welding an overlapped surface in an elliptical shape.

JP 2007-229740 A JP 2008-296236 A JP 2012-240083 A JP 2012-24008 A JP-A-2017-113781

  However, in the method described in Patent Literature 1, since the steel plate below the lap welding is protruded, the protruding portion becomes extra, and there is a problem that the part design is restricted.

  According to the method described in Patent Document 2, since laser is irradiated obliquely, if there is a gap in the overlapped plates, the melted portion is not formed well on the overlapped surface, and the penetration is insufficient, and the strength is secured. There is a problem that is difficult to do.

  In the methods described in Patent Literatures 3 and 4, there is a problem in that a portion once welded or the periphery of the welded portion is reheated or welded, so that reheating or welding requires more welding time.

  The method described in Patent Literature 5 welds an overlapped surface in an elliptical shape, and cannot be applied to a weld crack in a linear welded portion.

  The present invention has been made in view of the above-described problems, and a lap laser welded joint having good peel strength of a welded joint, capable of suppressing generation of a crack at an end portion of a molten portion and propagation of the crack, and a method of manufacturing the lapped laser welded joint And an automotive skeletal component having the lap laser welded joint.

  The present inventors have studied to solve the above-described problems, and have obtained the following findings.

In the present invention, (a) the total length of the fusion zone, (b) the length of the final weld, (c) the length, depth and width of the crater at the end of lap laser welding, and (d) a plurality of superposed sheets The thickness of the uppermost steel sheet among the steel sheets was noted. Then, by controlling all the relations (a) to (d) described above, that is, by forming a welded part satisfying the following equations (1) to (4) by lap laser welding, the end of the welded part is obtained. It was found that the generation of cracks on the side and the propagation of cracks could be suppressed. In the present invention, the fusion zone and the weld heat affected zone are collectively referred to as a weld zone.
L ≧ 15.0 (1)
10.0 ≧ L2 ≧ 2l _c (2)
t1 ≧ 2d _c (3)
w _c > d _c (4)
Here, L is the total length of the weld (Unit: mm), L2 is the length of the end welds (Unit: mm), _{l c} is the length of the crater end welds (Unit: mm), t1 is superimposed the thickness of the top layer of the steel sheet of the unit (unit: mm), d _c is the depth of the crater end welds (unit: mm), the w _c crater of the width of the end welds (unit: mm) is .

  Furthermore, by controlling the total thickness of the plurality of stacked steel sheets and the total size of the gap between the plurality of stacked steel sheets, it is possible to suppress the concentration of stress on the melted portion on the overlapped surface, and to peel off. It was found that the strength could be further improved.

The present invention has been completed based on the above findings, and has the following gist.
[1] A lap laser welded joint having a welded portion joined by lap laser welding to an overlapped portion where a plurality of steel plates are overlapped,
The welded portion includes a main welded portion penetrating the steel plate of the overlapped portion, and a final welded portion having a crater formed at one end of the main welded portion,
The welded portion is a lap laser welded joint satisfying the expressions (1) to (4).
L ≧ 15.0 (1)
10.0 ≧ L2 ≧ 2l _c (2)
t1 ≧ 2d _c (3)
w _c > d _c (4)
Here, L is the total length of the weld (Unit: mm), L2 is the length of the end welds (Unit: mm), _{l c} is the length of the crater end welds (Unit: mm), t1 is superimposed the thickness of the top layer of the steel sheet of the unit (unit: mm), d _c is the depth of the crater end welds (unit: mm), the w _c crater of the width of the end welds (unit: mm) is .
[2] The lap laser welded joint according to [1], wherein the sum of the sizes of the gaps between the steel plates in the overlapped portion is 0% or more and 15% or less with respect to the total thickness of the plurality of steel plates. .
[3] At least one steel plate among the plurality of steel plates is represented by mass%,
C: more than 0.07% and 0.25% or less
P + S: less than 0.03%,
Mn: 1.8% or more and 3.0% or less,
The lap laser welded joint according to the above [1] or [2], containing Si: more than 1.2% and not more than 2.5%, and having a component composition consisting of a balance of Fe and inevitable impurities.
[4] The lap laser welding according to any one of [1] to [3], further including one or two selected from the following group A and group B in addition to the component composition. Fittings.
Group A: mass%, one or two selected from Ti: 0.005% or more and 0.01% or less, and Nb: 0.005% or more and less than 0.050% Group B: mass% , Cr: 1.0% or less, Mo: 0.50% or less, and B: 0.10% or less [5] At least one steel sheet of the plurality of steel sheets Is a high-tensile steel plate having a tensile strength of 980 MPa or more, the lap laser welded joint according to any one of the above [1] to [4].
[6] The method for producing a lap laser welded joint according to any one of [1] to [5],
Plural steel plates are piled up and down,
A method of manufacturing a lap laser welded joint in which laser welding is performed by irradiating a laser beam to the surface of the uppermost steel sheet among the superposed portions of the plurality of superposed steel plates, and a welded portion is formed in the superposed portion and joined.
[7] The laser welding includes a main welding step of forming a main welding portion, and a final welding step of forming a final welding portion having a crater,
In order to form the welded portion satisfying the expressions (1) to (4),
Manufacturing of the lap laser welded joint according to [6], wherein at least one of a laser output, a welding speed, a focal position, and a beam diameter in the final welding step is controlled under a condition satisfying the expressions (5) to (7). Method.
L ≧ 15.0 (1)
10.0 ≧ L2 ≧ 2l _c (2)
t1 ≧ 2d _c (3)
w _c > d _c (4)
P _i ≧ P _f ≧ (1/4) P _i (5)
v _i ≧ v _f ≧ (1/4) v _i (6)
f _i ≦ f _f ≦ 20.0 (7)
Here, L is the total length of the weld (Unit: mm), L2 is the length of the end welds (Unit: mm), _{l c} is the length of the crater end welds (Unit: mm), t1 is superimposed the thickness of the top layer of the steel sheet of the unit (unit: mm), _{d c} is the depth of the crater end welds (unit: mm), _{w c} is crater of the width of the end welds (unit: mm), P _i the laser output of the welding process (unit: kW), laser output _{P f} is the final stage welding process (unit: kW), _{v i} is the welding speed of the welding process (unit: m / min), _{v f} is the final stage welding speed of the welding process (unit: m / min), _{f i} is the focal position of the welding process (unit: mm), _{f f} is the focal position of the end the welding process (unit: mm) is.
[8] A skeletal component for automobiles having the lap laser welded joint according to any one of [1] to [5].

  ADVANTAGE OF THE INVENTION According to this invention, since the generation | occurrence | production of a crack in the terminal part of a welding part and propagation of a crack in the lap laser welding of several superposed steel plates can be suppressed, the lap laser welding joint with favorable peel strength can be manufactured. . Further, the lap laser welded joint of the present invention is also excellent in appearance, so that it is suitable for structural members of automobiles, and a skeleton part for automobiles having the lap laser welded joint of the present invention can be manufactured.

FIG. 1 is a perspective view showing an example of the lap laser welded joint of the present invention. FIG. 2A is a schematic diagram illustrating a welding terminal portion of a conventional lap laser welding joint, and FIG. 2B is a schematic diagram illustrating a welding terminal portion of a lap laser welding joint of the present invention. FIG. 3A is a sectional view taken along line AA of the lap laser welded joint in FIG. 2A, and FIG. 3B is a sectional view taken along line BB of the lap laser welded joint in FIG. 2B. FIG. FIG. 4A is a top view and a sectional view illustrating a welded portion of a conventional lap laser welded joint, and FIG. 4B is a top view and a sectional view illustrating a welded portion of the lap laser welded joint of the present invention. It is. FIG. 5 is a perspective view illustrating a method for welding a lap laser welded joint according to the present invention. FIG. 6A is a top view illustrating the position of a welded portion (fused portion) of the lap laser welded joint of the present invention, and FIG. 6B is a cross-sectional view taken along line CC in FIG. 6A. . FIG. 7 is a diagram illustrating an example of the lap laser welded joint according to the embodiment of the present invention. FIG. 8 is a graph showing an example of lap laser welding conditions in the method of manufacturing a lap laser welded joint according to the present invention. FIG. 8A shows the relationship between laser output and welding time, and FIG. FIG. 8C shows the relationship between the speed and the welding time, and FIG. 8C shows the relationship between the focal position and the welding time.

  Hereinafter, a lap laser welded joint, a method of manufacturing a lap laser welded joint, and a skeleton part for an automobile will be described with reference to the drawings. Note that the present invention is not limited to this embodiment.

<Lap laser welded joint>
The lap laser welded joint of the present invention has a weld portion joined by lap laser welding to a lap portion where a plurality of steel plates are laid. The welded portion includes a main welded portion penetrating the steel plate of the overlapped portion, and a final welded portion having a crater formed at one end of the main welded portion, and the welded portion is defined by the following formulas (1) to (4). Satisfies the equation.
L ≧ 15.0 (1)
10.0 ≧ L2 ≧ 2l _c (2)
t1 ≧ 2d _c (3)
w _c > d _c (4)
Here, L is the total length of the weld (Unit: mm), L2 is the length of the end welds (Unit: mm), _{l c} is the length of the crater end welds (Unit: mm), t1 is superimposed the thickness of the top layer of the steel sheet of the unit (unit: mm), d _c is the depth of the crater end welds (unit: mm), the w _c crater of the width of the end welds (unit: mm) is .

  One embodiment of such a lap laser welded joint 1 of the present invention will be described with reference to FIGS. FIG. 1 is a perspective view showing an example of the lap laser welded joint 1 of the present invention. FIG. 2 (A) is a schematic diagram showing a welding terminal portion of a conventional lap laser welding joint, and FIG. 2 (B) is a schematic diagram showing a welding terminal portion of a lap laser welding joint of the present invention. 3A is a cross-sectional view taken along line AA shown in FIG. 2A, and FIG. 3B is a cross-sectional view taken along line BB shown in FIG. 2B. FIG. 4A is a top view and a sectional view showing a welded portion of a conventional lap laser welded joint, and FIG. 4B is a top view and a sectional view showing a welded portion of the lap laser welded joint of the present invention. .

  First, a lap laser welded joint 1 of the present invention will be described with reference to FIG.

  In the lap laser welded joint 1 of the present invention, at least two steel plates are overlapped. In the example shown in FIG. 1, a steel plate 2 having a substantially hat-shaped cross section and a flat panel-shaped steel plate 3 having a vertical wall portion 2 a and a flange portion 2 b extending outward from the tip of the vertical wall portion 2 a are provided. Use a steel plate. The steel plate 2 and the steel plate 3 are overlapped so as to face each other, and a region (flat region) of the flange portion 2b of the steel plate 2 is a joining surface. The two superposed steel plates 2 and 3 are joined by lap laser welding at the flange portion 2b. In the lap laser welding, a fusion part penetrating at least one of the steel plates 2 and 3 and joining the steel plates 2 and 3 is formed. The fusion zone and the weld heat affected zone of the fusion zone become the weld zone 4.

  The laser welding is performed by intermittently irradiating the laser beam 7 while moving the flange portion 2b in the longitudinal direction along the vertical wall portion 2a. Thereby, as shown in FIG. 1, a plurality of welds 4 having a substantially straight surface are formed on the joint surfaces of the steel plates 2 and 3. Here, as the lap laser welded joint 1 of the present invention, a case where two steel plates 2 and 3 are superposed will be described as an example, but three or more steel plates may be superposed.

  Next, the technical idea of the present invention and the configuration of the welded portion 4 will be described with reference to FIGS. FIGS. 2 (A), 3 (A) and 4 (A) show a welded portion 14 and its periphery in a conventional lap laser welded joint, respectively, in FIGS. 2 (B), 3 (B) and 4 (A). (B) shows the welded part 4 and its periphery in the lap laser welded joint of the present invention, respectively.

  In a conventional lap laser welding method, a weld is formed by welding at a constant output and speed. Therefore, the size of the keyhole, which is the controlling factor of the melt width, becomes the same size until the latter half of welding, and the welded portion 14 shown in FIG. 4A is generally formed. Specifically, the width W of the welded portion 14 is substantially the same from the start S to the end E of the welded portion 14. The steel plates 2 and 3 in the overlapped portion are melted through all of the steel plates 2 and 3 by welding. At the end E of the welded portion 14, a crater 15 having a large sectional area is formed on the upper steel plate 2.

In the lap laser welded joint welded by the above-described conventional lap laser welding method, the depth of the crater 15 at the end of the welded portion 14 is greater than the thickness of the uppermost steel plate. Specifically, as shown in FIG. 2 (A) and FIG. 3 (A), the depth d _c of the crater 15 penetrates the steel plate 2, the more the thickness of the steel plate 2. In the case of such a shape, a tensile stress (force in the direction of arrow Fa shown in FIG. 2A) directed outward from the outer peripheral portion of the fusion zone is applied to the central portion, which is the final solidified portion, at the end E of the welded portion 14. Concentrate and take. As a result, it has been found that solidification cracks 16 may be generated and propagated at the end portion of the welded portion 14.

  On the other hand, in the lap laser welding method for forming the shape of the welded portion 4 of the present invention to be described later, the width W of the welded portion 4 is a predetermined width from the starting end S of the welded portion 4 as shown in FIG. It is formed substantially the same up to the position, but is formed so as to be gradually narrowed from the predetermined position to the end E. The steel plates 2 and 3 in the overlapped portion are melted by penetrating all of the steel plates 2 and 3 in the first half of the welding to the above-described predetermined position, but in the second half of welding after the above-described predetermined position, the lower steel plate 3 is melted. Is reduced. At the end E of the weld 4, a small crater 5 is formed on the upper steel plate 2.

As shown in FIGS. 4A and 4B, the size of the crater 5 formed at the end E of the welded portion 4 is smaller than the thickness of the uppermost steel plate as compared with the conventional crater 15. (Shallow). Specifically, as shown in FIG. 2 (B) and FIG. 3 (B), the depth d _c of the crater 5 is shallow, not penetrate the steel plate 2. In the case of such a shape, at the terminal end E of the welded portion 4, the central portion (the final solidification of the terminal end E) of the tensile stress (force in the direction of the arrow Fb shown in FIG. Concentration in the center of the part). Thereby, it is possible to prevent the occurrence of solidification cracking at the terminal portion of the welded portion 4.

  Based on the above technical idea, in the lap laser welded joint 1 of the present invention, the surface dimensions of the welded portion 4 are adjusted to a predetermined range. In particular, it is important to reduce the size of the crater 5 at the welding end.

  Specifically, as shown in FIG. 4B, the welded portion 4 includes a main welded portion 4a penetrating the steel plate of the overlapped portion, and a crater 5 formed continuously from one end of the main welded portion 4a. And a final weld 4b. The welded portion 4 satisfies the above equations (1) to (4).

(Overall length L (mm) of welded portion 4: L ≧ 15.0 mm)
If the total length L of the welded portion 4 is shorter than 15.0 mm, the length L2 (mm) of the final welded portion 4b described later cannot be sufficiently secured, and a weld crack occurs. Therefore, the total length L of the welded portion 4 is 15.0 mm or more (formula (1)). Preferably, it is 20.0 mm or more. Although the upper limit of the total length L of the welded portion 4 is not particularly defined, it is preferably 40.0 mm or less from the viewpoint of preventing the welding time of parts from becoming long. More preferably, it is 30.0 mm or less.

(Length L2 (mm) of final weld 4b: 10.0 ≧ L2 ≧ 2l _c )
The length l _c of the crater 5 telophase welded portion 4b, if larger than 1/2 of the length L2 of the end welds 4b, because of the large proportion of craters 5 against end portions of the weld 4 (final weld 4b) In addition, the occurrence of welding cracks cannot be suppressed. Therefore, the length _{l c} of the crater 5 telophase welded portion 4b is set to 1/2 or less of the length of the end weld 4b L2 (mm). That is, the length L2 of the end welds 4b is at least twice the length _{l c} of the crater 5 telophase welded portion 4b (above (2)). It is preferably at least 7.0 mm. The upper limit of the length L2 of the final weld 4b is set to 10.0 mm or less from the viewpoint of suppressing the occurrence of welding cracks. Preferably, it is 9.5 mm or less.

(Thickness of the uppermost layer of the steel sheet of the overlapping portions _{t1 (mm): t1 ≧ 2d} c)
The depth d _c of the crater 5 telophase welded portion 4b, if larger than 1/2 of the plate thickness of the steel sheet of the uppermost layer of the overlapping portions (the uppermost part of the partial superposition a plurality of steel plates) t1 In addition, underfill on the surface of the steel sheet becomes remarkable. As a result, the tensile stress is more concentrated on the terminal end E of the welded portion 4, and the welding crack is easily generated. Further, when welding cracks occur, as shown in Examples of the present invention described later, in a test for evaluating the peel strength, the fracture is likely to occur from the weld crack portion, and the peel strength intended in the present invention cannot be obtained. Sometimes. Therefore, to 1/2 or less of the plate thickness of the top layer of the steel sheet within a depth of crater 5 d _c is overlapping portions of the end weld 4b t1 (mm). That is, the thickness t1 of the top layer of the steel sheet of the overlapping portions is at least twice the depth d _c of the crater 5 telophase weld 4b (above (3)).
In the following description, the “plate thickness t1 of the uppermost steel plate in the overlapped portion” corresponds to “t2” in the drawing in the case of the example shown in FIG. 4B.

In the present invention, is not particularly a lower limit of the depth d _c of the crater 5 telophase weld 4b defines, from the viewpoint of the real construction, the depth d _c of the crater 5 telophase weld 4b, of the superposed parts It is preferable that the thickness be equal to or less than 1/3 of the thickness t1 (mm) of the uppermost steel sheet. That is, the thickness t1 of the top layer of the steel sheet of the overlapping portions is preferably three times or more the depth d _c of the crater 5 telophase weld 4b (3d _c ≦ t1). More preferably, the thickness t1 of the uppermost steel sheet in the overlapped portion is 0.7 mm or more.
From the viewpoint of performing the welding without reducing the laser output as much as possible efficiently, the depth d _c of the crater 5 telophase welding unit 4b, the thickness of the top layer of the steel sheet of the overlapping portions t1 (mm) 1 / 10 or more is preferable. That is, the thickness t1 of the top layer of the steel sheet of the overlapping portions is preferably set to 10 times the depth d _c of the crater 5 telophase weld _{4b (10 × d c ≧ t1} ).

(Width _w c (mm crater 5 telophase weld _{4b): w c> d c} )
Also the depth d _c of the crater 5 telophase welded portion 4b is not more than 1/2 of the plate thickness t1 of the top layer of the steel sheet of the overlapping portion as described above, the depth d _c of the crater 5 telophase weld 4b There the case of more than the width w _c of the crater 5 telophase weld 4b, since the underfill in the steel sheet surface becomes significantly more concentrated tensile stress at the end E of the welded portion 4, weld cracking is likely to occur . Further, when a weld crack occurs, as shown in the examples described later, in a test for evaluating the peel strength, breakage easily occurs from the weld crack portion, and the peel strength intended in the present invention may not be obtained. . Therefore, the depth d _c of the crater 5 telophase welded portion 4b is smaller than the width w _c of the crater 5 telophase weld 4b. That is, the width _{w c} of the crater 5 telophase welded portion 4b is larger than the depth _{d c} of the crater 5 telophase welded portion 4b (equation (4)). Preferably, the width _{w c} of the crater 5 telophase weld 4b shall be 0.15mm or more.
Incidentally, in particular lower limit of the depth d _c of the crater 5 telophase weld 4b is not specified, from the viewpoint of the real construction, preferably 0.30mm or more.
Incidentally, the size of the crater 5 telophase welded portion 4b increases, the underfill is increased, the width w _c of the crater 5 telophase weld 4b is preferably set to 2mm or less.

  As described above, since the welded portion 4 of the present invention forms the main welded portion 4a and the final welded portion 4b in the above-described predetermined ranges, the above-described effects of reducing the size of the crater 5 are maximized. I can put it out. As a result, excessive stress concentration on the terminal end E of the welded portion 4 can be prevented, and the occurrence of welding cracks can be prevented. Thereby, even if the minimum value of the total length L of the welded portion 4 is as short as 15.0 mm, it is possible to prevent the occurrence of welding defects at the end of the welded portion.

  The lap laser welded joint 1 of the present invention can obtain the desired characteristics in the present invention with the above-described configuration. However, in addition to the above-described configuration, the following configuration can be added as needed.

(Total thickness of gap (mm) between steel plates with respect to total thickness T (mm) of a plurality of steel plates: 0% or more and 15% or less)
In the present invention, the total G of the gaps between the steel plates (hereinafter, sometimes referred to as a total plate gap) in a superposed portion where a plurality of steel plates are superimposed is represented by a total plate thickness T ( mm) to 0% or more and 15% or less. In the example shown in FIG. 4B, the gap between the steel plates (gap) is only between the steel plates 2 and 3, so that the total plate gap is Gmm and the total plate thickness T of the plurality of steel plates is (t2 + t3). ) Mm, 0% ≦ G / (t2 + t3) ≦ 15%. By adjusting the total gap G (mm) with respect to the total thickness T (mm) of the plurality of steel sheets to the above-described range, the amount of underfill is suppressed, and the stress concentration on the welded portion formed on the overlapped surface is reduced. As a result, welding cracks can be suppressed, and the peel strength can be further improved. More preferably, the total gap G (mm) with respect to the total thickness T (mm) of the plurality of steel plates is 5% or more. More preferably, it is set to 10% or less.

(Steel composition)
Although the component composition of the steel sheet used for the lap laser welded joint 1 of the present invention is not particularly limited, the component composition of at least one of the steel sheets to be superposed is, for example, C: more than 0.07% by mass%. 0.25% or less, P + S: less than 0.03%, Mn: 1.8% or more and 3.0% or less, Si: 1.2% or more and 2.5% or less, the balance being Fe and unavoidable impurities It can have a component composition. Hereinafter,% in each component composition means mass%.

(C: more than 0.07% and 0.25% or less)
When the C content exceeds 0.07%, the effect of precipitation strengthening can be obtained. On the other hand, when the C content is 0.25% or less, it is possible to ensure desired high strength and workability without causing precipitation of coarse carbides. Therefore, the C content is preferably set to be more than 0.07% and 0.25% or less. More preferably, the C content is 0.10% or more and 0.21% or less.

(P + S: less than 0.03%)
When the total amount (P + S) of the P content and the S content is less than 0.03%, the toughness does not decrease and the desired high strength and workability can be secured. Therefore, the total amount (P + S) of the P content and the S content is preferably less than 0.03%.

(Mn: 1.8% or more and 3.0% or less)
When the Mn content is 1.8% or more, sufficient hardenability can be secured, so that coarse carbides are less likely to precipitate. On the other hand, when the Mn content is 3.0% or less, the susceptibility to grain boundary embrittlement increases, and the toughness and low-temperature crack resistance hardly deteriorate. Therefore, it is preferable that the Mn content be 1.8% or more and 3.0% or less. More preferably, the Mn content is 1.9% or more. The Mn content is more preferably not more than 2.7%, and still more preferably not more than 2.5%.

(Si: more than 1.2% and 2.5% or less)
When the Si content is more than 1.2%, the effect of forming a solid solution to increase the strength of steel can be sufficiently obtained. On the other hand, when the Si content is 2.5% or less, the hardening of the heat affected zone hardly increases, and the toughness and low temperature crack resistance of the heat affected zone hardly deteriorate. Therefore, it is preferable that the Si content be more than 1.2% and not more than 2.5%. More preferably, the Si content is 1.3% or more and 1.5% or less.

(Remainder Fe and inevitable impurities)
The balance other than the above composition is Fe and inevitable impurities. Examples of the inevitable impurities include Al: 0.015 to 0.050%, and N: 0.002 to 0.005%.

  In addition, in order to further improve the strength of the steel sheet and the peel strength, one or two selected from the following groups A and B can be further contained, if necessary, in addition to the above-described component composition.

(Group A: one or two selected from Ti: 0.005% or more and 0.01% or less, and Nb: 0.005% or more and less than 0.050% by mass%)
Ti and Nb precipitate as carbides or nitrides, and have an effect of suppressing austenite coarsening during annealing. Therefore, when Ti and Nb are contained, it is preferable to contain at least one kind. When Ti and Nb are contained in order to obtain this effect, it is preferable that Ti contains 0.005% or more and Nb contains 0.005% or more, respectively. However, even if these elements are excessively contained, the effect of the above-described action may be saturated and uneconomical. In addition, the recrystallization temperature during annealing rises, the metal structure after annealing becomes uneven, and the stretch flangeability may be impaired. Furthermore, there is a possibility that the precipitation amount of carbide or nitride increases, the yield ratio increases, and the shape freezing property also deteriorates. Therefore, when Ti and Nb are contained, the Ti content is preferably 0.01% or less and the Nb content is preferably less than 0.050%. More preferably, the Ti content is less than 0.0080%. More preferably, the Nb content is less than 0.040%.

(Group B: by mass%, one or more selected from Cr: 1.0% or less, Mo: 0.50% or less, and B: 0.10% or less)
Cr, Mo and B are elements having an effect of improving the hardenability of steel. Therefore, one or more of these elements may be contained. However, even if these elements are excessively contained, the above-mentioned effects may be saturated and uneconomical. Therefore, when Cr, Mo and B are contained, the Cr content is 1.0% or less, the Mo content is 0.50% or less, and the B content is 0.10% or less, respectively. More preferably, the Cr content is 0.50% or less. More preferably, the Mo content is 0.10% or less. More preferably, the B content is 0.03% or less, and still more preferably, the B content is 0.0030% or less. Preferably, the Cr content is 0.01% or more. Preferably, the Mo content is 0.004% or more. Preferably, the B content is 0.0001% or more.

(Tensile strength of steel sheet)
Among the plurality of steel plates used for the lap laser welded joint 1 of the present invention, at least one steel plate can be a high-tensile steel plate having a tensile strength TS of 980 MPa or more. Even if at least one steel plate is the above-described high-tensile steel plate, the lap laser welded joint 1 can obtain high joining strength and can prevent occurrence of welding defects. For example, it is preferable that at least one steel plate among the plurality of steel plates has the above-described composition and has a tensile strength TS of 980 MPa or more. The plurality of steel plates may be the same type and the same shape, or may be different types and different shapes.

(Sheet thickness of steel plate)
In the present invention, the thickness t of the plurality of steel plates to be subjected to the lap laser welding is not particularly limited, but is preferably, for example, in a range of 0.5 mm ≦ t ≦ 3.2 mm. A steel sheet having a thickness in this range can be suitably used as an automobile outer panel and an automobile frame member. The thicknesses of the plurality of steel plates may all be the same or may be different.

  Specifically, in the case of the lap laser welded joint 1 shown in FIG. 1 and the like, the thickness t2 of the upper steel plate 2 satisfies 0.6 mm ≦ t2 ≦ 1.2 mm, and the thickness of the lower steel plate 3 It is preferable that t3 is 1.0 mm ≦ t3 ≦ 2.5 mm. Alternatively, it is preferable that the thickness t2 of the upper steel plate 2 and the thickness t3 of the lower steel plate 3 both satisfy the ranges of 0.5 mm ≦ t2 ≦ 3.2 mm and 0.5 mm ≦ t3 ≦ 3.2 mm. .

  In the present invention, the term “weld crack” refers to a low-temperature crack that occurs at the welding end of the welded portion 4 and propagates from the welding end E to the welding start S. The presence or absence of a weld crack can be determined by cutting the welded portion 4 after welding and confirming the presence or absence of a crack. The presence or absence of cracks can also be confirmed visually. From the viewpoint of more clearly discriminating, for example, it is preferable to confirm the cut surface of the welded portion by magnifying it about 10 times with an optical microscope. When taking a photograph of the cross section of the welded portion, a portion 5 mm away from the end of welding is cut out perpendicular to the welding direction by a precision cutting machine. In addition, welding cracks are observed penetrating from the front surface to the back surface of the welded portion 4.

<Production method of lap laser welded joint>
First, a method for manufacturing the above-described lap laser welded joint 1 of the present invention will be described with reference to FIG. FIG. 5 is a diagram for explaining an example of a welding method for the lap laser welded joint 1 of the present invention.

  The method for manufacturing a lap laser welded joint 1 of the present invention is the method for manufacturing the lap laser welded joint 1 described above, wherein a plurality of steel plates are vertically stacked, and then a superposed portion of the plurality of superposed steel plates is formed. Of these, lap laser welding is performed by irradiating a laser beam to the uppermost steel sheet surface, and a weld 4 is formed at the overlapped portion and joined.

  In the present invention, one-side welding is performed on a plurality of stacked steel plates. By performing the one-side welding, it is possible to realize space saving of an automobile body parts assembly line. In the one-side welding, it is preferable to perform lap laser welding from the side of the steel plate having a larger thickness among the plurality of stacked steel plates. Thereby, burn-through can be prevented. When the steel plates have the same thickness, laser welding may be performed in order from either side.

  In the example shown in FIG. 5, the lap laser welded joint 1 of the present invention superimposes a plurality of steel plates 2 and 3 and forms a straight line on the surface of the outermost steel plate 2 so as to form a weld 4 on the steel plates 2 and 3. It can be obtained by performing lap laser welding of irradiating a laser beam 7 in a shape.

  In the lap laser welding described above, the laser beam 7 is continuously irradiated while scanning linearly. For example, as shown in FIG. 5, the main weld 4a and the final weld 4b are continuously formed to form the weld 4. In this case, the effect of reducing the size of the crater 5 can be maximized by continuously performing the final welding step of forming the final weld 4a and the final welding step of forming the final weld 4b. Therefore, it is preferable because excessive stress concentration on the terminal end E of the welded portion 4 (see FIGS. 2B and 3B) can be prevented, and occurrence of cracks can be prevented.

  The lap laser welding according to the present invention includes a main welding step for forming the main weld 4a and a final welding step for forming the final weld 4b having the crater 5. The main welding step is main welding that penetrates all of the steel plates in the overlapped portion in the first half of welding. The final welding step is intended to reduce the size of the crater 5 formed at the end E of the welded part 4 while adjusting welding conditions to be described later up to the end E of the welded part 4 following the main welding step. This is the final welding performed. The laser output, the welding speed, the focal position, and the focal position of the final welding step so that the final weld 4a having the main weld 4a and the crater 5 forms the weld 4 satisfying the above equations (1) to (4). Preferably, at least one of the beam diameters is controlled. In this welding step, welding is performed under certain conditions.

  For example, a fiber laser, a disk laser, or the like can be used as the laser beam. In addition, beam diameter: 0.3 to 0.8 mm, laser output: 2.0 to 5.0 kW, focal position: range from on the outermost layer surface of the steel sheet to 0 to 20 mm above the outermost layer surface of the steel sheet, welding speed: It is preferable to be 2.0 to 5.0 m / min.

More preferably, in forming the main welded portion 4a, the beam diameter is 0.5 to 0.8 mm, the laser output is 2.5 to 4.5 kW, and the focal position is 20 mm from the surface of the outermost layer of the steel sheet. It is preferable to control in the range up to the upper side and the welding speed: in the range of 2.5 to 4.5 m / min.
In forming the final weld 4b, the beam diameter is 0.2 to 0.6 mm, the laser output is 0.5 to 3.0 kW, and the focal point is from the surface of the outermost layer of the steel plate to 30 mm above the surface of the outermost layer of the steel plate. And the welding speed is preferably controlled in the range of 2.0 to 4.0 m / min.

More preferably, the relationship between the laser output Pi, the welding speed vi, and the focal position fi in the main welding process and the laser output Pf, the welding speed vf, and the focal position ff in the final welding process are as shown in FIGS. It is preferable to control the laser output, the welding speed, and the focal position so as to satisfy the relationship shown in each graph of C). Specifically, at least one of the laser output, the welding speed, the focal position, and the beam diameter in the final welding step can be controlled under the conditions satisfying Expressions (5) to (7).
P _i ≧ P _f ≧ (1/4) P _i (5)
v _i ≧ v _f ≧ (1/4) v _i (6)
f _i ≦ f _f ≦ 20.0 (7)
Here, laser output _{P i} is the welding process (unit: kW), laser output _{P f} is the final stage welding process (unit: kW), _{v i} is the welding speed of the welding process (unit: m / min), v _f is the welding speed of the final welding process (unit: m / min), _{f i} is the focal position of the welding process (unit: mm), _{f f} is the focal position of the end the welding process (unit: mm) is.

P _i ≧ P _f ≧ (1/4) P _i (5)
If the laser output P _f (kW) in the final welding step exceeds the laser output P _i (kW) in the main welding step, the underfill increases and burnout may occur. Even more preferably, the laser output _{P f} of the final welding process is less (Pi × 0.5).

On the other hand, the laser output P _f of the final welding process, of less than 1/4 of the laser power P _i of the welding process, the laser power can not dissolve the steel sheet insufficient. For this reason, a sufficient welding line length cannot be secured, and the peel strength may be insufficient. Even more preferably, the laser output _{P f} of the final welding step is set to (Pi × 1/3) or more.

v _i ≧ v _f ≧ (1/4) v _i (6)
Welding speed telophase welding process _v f (m / min) is, if more than welding speed _v i of the welding process (m / min), the depth _{d c} of the crater 5 telophase welded portion 4b may become deeper . Even more preferably, the welding speed _{v f} of the final welding process is less _{(v i} × 0.8).

On the other hand, the welding speed v _f of the final welding process, of less than 1/4 of the welding speed v _i of the welding process, the size of the crater 5 telophase welded portion 4b is increased, there is a possibility that burn-occurs . Even more preferably, the welding speed _{v f} of the final welding step and _{(v i} × 1/2) or more.

f _i ≦ f _f ≦ 20.0 (7)
Focus position _f f telophase welding process (mm) is, if less than the focal position _f i of the welding process (mm), there is a possibility that the depth _{d c} of the crater 5 telophase welded portion 4b becomes deep. Even more preferably, the focal position _{f f} telophase welding process and _{(f i} × 1.2) or more.

On the other hand, the focal position f _f telophase welding process, if it exceeds 20.0 mm, power density of the laser is unable to dissolve the steel sheet insufficient. For this reason, a sufficient welding line length cannot be secured, and the peel strength may be insufficient. Even more preferably, the focal position _{f f} telophase welding process is not more than 15.0 mm.

  Further, in the welding method of the present invention, as the steel plates 2 and 3, for example, a steel plate having the above-described component composition and having a tensile strength TS of 980 MPa or more can be used. The thicknesses t2 and t3 of the plurality of steel plates 2 and 3 are 0.5 mm ≦ t2 ≦ 3.2 mm and 0.5 mm ≦ t3 ≦ 3.2 mm, respectively. 3 can be 0% or more and 15% or less of the total thickness. The reason for applying these steel plates is the same as described above.

  Next, an example of a suitable welding position in the lap laser welded joint 1 of the present invention will be described with reference to FIG.

  Drawing 6 is a figure explaining an example of a position of suitable welding part (fusion part) 4 in lap laser welding joint 1 of the present invention. FIG. 6A is a top view showing the periphery of the welded portion 4 of the two steel plates 2 and 3, and FIG. 6B is a cross-sectional view taken along line CC of FIG. 6A. In the description of FIG. 6, the steel plate 2 is also referred to as a flange portion 2b, and the steel plate 3 is also referred to as a frame part.

In the example shown in FIGS. 6A and 6B, the position coordinate of the end of the contact position between the flange portion 2 b of the upper steel plate 2 and the frame component of the lower steel plate 3 is set to 0. Further, the outer end side of the flange portion 2b is (-), and the vertical wall portion 2a side in the substantially hat shape (only a part of the substantially hat shape is shown in FIG. 6) is (+). Expressed by In the substantially hat-shaped flange portion 2b, the thickness of the steel plate at the thickest portion is t (mm). At this time, it is preferable to apply the one-sided welding method at a welding position X (mm) represented by the following equation (8) and perform welding. Thereby, as shown in FIG. 7, the peel strength of an L-shaped tensile test piece having a total plate thickness T of 2 to 5 mm and a length of the flange portion 2b of 50 mm in a two-ply configuration is set to 1.2 kN or more. Can be.
−2t ≧ X ≧ −4t (8)
Here, the reason why X is set as in the above equation (8) will be described.

  If the welding position X is closer to the contact end of the flange portion 2b than -2t, the welding position X may be more easily broken than the welded metal portion during a tensile test, and the peel strength may be lower. On the other hand, when the welding position X is farther from the contact end of the flange portion 2b than -4t, the moment applied to the welded portion 4 tends to increase, and the peel strength may decrease. Therefore, it is preferable that the welding position X be set as in the above equation (8).

<Automotive frame parts>
An example of a part that can suitably use the lap laser welded joint 1 of the present invention is a skeleton part for an automobile. In the case of the skeleton part for an automobile shown in FIG. 1 described above, a steel plate 2 which is a frame part having a substantially hat-shaped cross section and a steel plate 3 which is a panel part are used. The skeleton part for an automobile is obtained by welding the flange part 2b of the frame part (steel plate 2 shown in FIG. 1) and the panel part (steel plate 3 shown in FIG. 1) disposed opposite to the flange part 2b by the above-described welding method. A closed cross section is formed by welding to form the above-described welded portion 4.

  It is preferable to apply the automotive skeleton component of the present invention to, for example, a center pillar, a roof rail, and the like. For these components, it is important to ensure peel strength from the viewpoint of collision safety. The center pillar to which the automobile frame part of the present invention is applied has a sufficient peel strength as described above.

  As described above, according to the present invention, a plurality of steel sheets including at least one high-strength steel sheet are overlapped, a welded portion 4 is formed and welded, whereby welding defects occur on the front and back surfaces of the steel sheet. It is possible to obtain a lap laser welded joint 1 without performing.

  In the weld 4 of the present invention, the size of the crater at the end of the fusion zone can be reduced, so that the concentration of tensile stress at the center of the final solidification zone decreases. As a result, generation and propagation of cracks at the end of the fusion zone can be suppressed, so that the lap laser welded joint 1 having high peel strength and excellent durability can be manufactured.

  Further, even if the fusion zone length (15 mm) is shorter than that of conventional lap laser welding, welding cracks can be suppressed. For this reason, improvement in the degree of freedom of member design and improvement in strength by welding a large number of parts requiring more peel strength can be expected.

  Furthermore, since the lap laser welded joint 1 of the present invention is excellent in appearance, it can be suitably used for structural members of automobiles. For example, by using a high-strength steel plate as a steel plate to be joined, a skeleton part for an automobile can be obtained. By using such a lap laser welded joint 1, it is possible to obtain an automobile skeleton part having a high peel strength.

  Hereinafter, the operation and effect of the present invention will be described using examples. Note that the present invention is not limited to the following embodiments.

  In this example, a steel sheet having a component composition shown in Table 1 was used as a test material.

  The plate thickness of the steel plate is any of 1.2 mm, 1.6 mm and 2.0 mm, and the plate width is 50 mm. Using these steel plates, as shown in FIG. 7, an L-shaped cross-section was bent. The L-shaped steel plate 8 has a long side 8a and a short side 8b. The long side 8a corresponds to the vertical wall 2a of the steel plate 2 of the lap laser welded joint 1 shown in FIG. 1, and the short side 8b corresponds to the flange 2b.

  Then, two L-shaped steel plates 8 of the same steel type and the same plate thickness were used, and the short sides 8b were overlapped with each other. Thereafter, the overlapped portion (the flat portion shown in FIG. 7) is intermittently overlapped at a plurality of locations in the longitudinal direction and laser welding is performed to form a weld bead (welded portion 4), and an L-shaped test piece (hereinafter, a test piece) is formed. ). Here, the test piece size was such that the long side 8a (vertical wall length) was 120 mm, the short side 8b (test piece width) was 50 mm, and the overlapped portion (flange width) was 30 mm. The gap (gap) G between the upper and lower L-shaped steel plates 8 was appropriately adjusted within a range of 0 to 20% in accordance with the thickness of the plate.

Table 2-1 and Table 2-2 show the conditions of the welded portion 4 formed by lap laser welding.
As shown in FIG. 7, the coordinates indicating the welding position are such that the contact position closer to the vertical wall in the portion where the two L-shaped steel plates 8 are overlapped is 0, and the outside of the overlapped portion of the test pieces is (−). ), The vertical wall side of the test piece is represented by (+) coordinate system. The welding position at this time is X, the total length of the welded portion (welded portion) 4 is L, the length of the terminal end of the welded portion 4 (final welded portion 4b) is L2, and the length of the crater 5 of the final welded portion 4b is l _c. The depth of the crater 5 of the final weld 4b was set to d _c , and the width of the crater 5 of the final weld 4b was set to w _c, and the test was performed by variously changing the values.

  For laser welding, a fiber laser having a beam diameter of 0.6 mmφ at the focal position was used. The size of the crater 5 of the final welding portion 4b is determined by the main welding process and the final welding so that the laser output, the welding speed, and the focal position have the relationships shown in the graphs of FIGS. Adjusted in the process. The processing point distance was on the outermost layer surface of the steel sheet. The focal position of the lap laser welding is set such that the uppermost steel sheet surface (the surface of the upper L-shaped steel sheet 8 in the example shown in FIG. The upward direction was positive. Welding was performed in air.

  The peel strength was measured by an L-shaped tensile test in which the steel plates 8 bent in an L-shape were overlapped with each other as shown in FIG. 7 and subjected to lap laser welding, and a tensile load was applied from both sides of the welded steel plates. The tensile test was performed at a speed of 10 mm / min based on JIS Z3136. In the evaluation of the peel strength, when the peel strength was 1.2 kN or more, it was evaluated as “pass” as having high bonding strength.

  Further, the occurrence of cracks can be determined visually and by a penetration test. In this embodiment, as described above, the occurrence of cracks was visually determined. Specifically, a position 5 mm away from the center of the crater 5 of the final welded portion 4b toward the welding start side from the center of the crater 5 was cut from the obtained test piece in a direction perpendicular to the welding direction. The cut surface was confirmed by magnifying 10 times with an optical microscope. One observation was made under each condition. When it penetrated from the front surface to the back surface of the welded portion 4, it was determined that there was a weld crack.

  Table 2-1 and Table 2-2 show the obtained determination results of the weld crack and the peel strength.

  As shown in Table 2-1 and Table 2-2, the test piece of the present invention example had a peel strength of 1.2 kN or more and did not generate welding defects.

On the other hand, among the test pieces of the comparative examples, 2, No. 10, No. 18, No. 26, no. 34, no. 42 Soitasuki G is greater than 15% of the SoitaAtsu T, for further deep depth d _c of the crater 5 end E of the welded portion 4 (the larger the value), weld cracking occurs.

  In addition, No. 4, no. 12, No. 20, no. 28, no. 36, no. In No. 44, since the total length L of the welded portion 4 was shorter than 15.0 mm, welding cracks occurred.

  In addition, No. 5, no. 13, No. 21, no. 29, no. 37, no. In No. 45, since the length L2 of the final weld 4b was small, welding cracks occurred.

In addition, No. 6, no. 14, No. 22, no. 30, no. 38, no. 46, the depth d _c of the crater 5 end E of the welded portion 4 is deep (greater value), the weld cracking occurs.

In addition, No. 7, no. 15, No. 23, no. 31, No. 39, no. 47, due to the large length l _c of the crater 5 end E of the welded portion 4, weld cracking occurs.

In addition, No. 8, No. 16, No. 24, no. 32, no. 40, no. 48, since the width w _c of the crater 5 end E of the welded portion 4 is small, weld cracking occurs.

  As described above, in the example of the present invention in which lap laser welding was performed according to the above-described present invention, a good lap laser welded joint having the characteristics intended in the present invention was obtained. On the other hand, in the comparative example of the present invention which deviates from the above welding conditions, it can be seen that a good lap laser welded joint was not obtained.

1 lap laser weld joint 2 steel plate 3 steel plate 4 welded portion 4a present welded portion 4b of the final weld 5 crater 7 laser beam 8 steel 14 overall length L2 end welds of the welded portion 15 crater 16 Cracking L weld length l _c crater width G Itasuki width W weld depth w _c crater length d _c crater

Claims (8)

A lap laser welded joint having a welded portion joined by laser welding to an overlapped portion obtained by overlapping a plurality of steel plates,
The welded portion includes a main welded portion penetrating the steel plate of the overlapped portion, and a final welded portion having a crater formed at one end of the main welded portion,
The welded portion is a lap laser welded joint satisfying the expressions (1) to (4).
L ≧ 15.0 (1)
10.0 ≧ L2 ≧ 2l _c (2)
t1 ≧ 2d _c (3)
w _c > d _c (4)
Here, L is the total length of the weld (Unit: mm), L2 is the length of the end welds (Unit: mm), _{l c} is the length of the crater end welds (Unit: mm), t1 is superimposed the thickness of the top layer of the steel sheet of the unit (unit: mm), d _c is the depth of the crater end welds (unit: mm), the w _c crater of the width of the end welds (unit: mm) is .   2. The lap laser welded joint according to claim 1, wherein the sum of the sizes of the gaps between the steel plates in the overlapped portion is 0% or more and 15% or less with respect to the total thickness of the plurality of steel plates. At least one steel sheet of the plurality of steel sheets is, by mass%,
C: more than 0.07% and 0.25% or less
P + S: less than 0.03%,
Mn: 1.8% or more and 3.0% or less,
The lap laser welded joint according to claim 1 or 2, wherein the lap laser welded joint contains Si: more than 1.2% and not more than 2.5%, and has a component composition consisting of the balance of Fe and inevitable impurities. The lap laser welded joint according to any one of claims 1 to 3, further comprising one or two selected from the following group A and group B in addition to the component composition.
Group A: mass%, one or two selected from Ti: 0.005% or more and 0.01% or less, and Nb: 0.005% or more and less than 0.050% Group B: mass% , Cr: 1.0% or less, Mo: 0.50% or less, and B: 0.10% or less   The lap laser welded joint according to any one of claims 1 to 4, wherein at least one of the plurality of steel plates is a high-tensile steel plate having a tensile strength of 980 MPa or more. It is a manufacturing method of the lap laser welding joint according to any one of claims 1 to 5,
Plural steel plates are piled up and down,
A method of manufacturing a lap laser welded joint in which laser welding is performed by irradiating a laser beam to the surface of the uppermost steel sheet among the superposed portions of the plurality of superposed steel plates, and a welded portion is formed in the superposed portion and joined. The laser welding has a main welding step of forming a main welding portion, and a final welding step of forming a final welding portion having a crater,
In order to form the welded portion satisfying the expressions (1) to (4),
The production of the lap laser welded joint according to claim 6, wherein at least one of a laser output, a welding speed, a focal position, and a beam diameter in the final welding step is controlled under a condition satisfying Expressions (5) to (7). Method.
L ≧ 15.0 (1)
10.0 ≧ L2 ≧ 2l _c (2)
t1 ≧ 2d _c (3)
w _c > d _c (4)
P _i ≧ P _f ≧ (1/4) P _i (5)
v _i ≧ v _f ≧ (1/4) v _i (6)
f _i ≦ f _f ≦ 20.0 (7)
Here, L is the total length of the weld (Unit: mm), L2 is the length of the end welds (Unit: mm), _{l c} is the length of the crater end welds (Unit: mm), t1 is superimposed the thickness of the top layer of the steel sheet of the unit (unit: mm), _{d c} is the depth of the crater end welds (unit: mm), _{w c} is crater of the width of the end welds (unit: mm), P _i the laser output of the welding process (unit: kW), laser output _{P f} is the final stage welding process (unit: kW), _{v i} is the welding speed of the welding process (unit: m / min), _{v f} is the final stage welding speed of the welding process (unit: m / min), _{f i} is the focal position of the welding process (unit: mm), _{f f} is the focal position of the end the welding process (unit: mm) is.   An automotive skeletal component having the lap laser welded joint according to any one of claims 1 to 5.

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